Mechanical drive trains use gears, shafts, gearboxes, pulleys and the like to transmit power from a "prime mover," e.g., an electric motor or internal combustion engine, to an end-use function. All such drive trains use a number of bearings and, often, such bearings are of differing types. For example, the output shaft of an electric motor, considered a high speed shaft, is supported on ball, roller or some other type of so-called hydrodynamic bearing. Such bearings are so named because of the way their surfaces are "self-lubricated" as they roll.
At other locations, such drive trains may use what are called bushing-type or plain journal bearings. Journal bearings do not use rolling balls or cylinders. Rather, they are simply cylindrical tubes, with or without flanged ends, and are often made of brass or bronze. Journal bearings, said to be "boundary lubricated," are used in drive train applications where relative rotational speed is quite low and where the bearing and shaft through the bearing are subjected to high-impact, tipping or bending loads or a combination of such loads.
Journal bearings (which are fitted over a shaft) are often fitted into a surrounding housing. To put it another way, the bearing is interposed between a shaft and a housing, the latter "reinforcing" and supporting the bearing against loads imposed on it by the shaft. However, the housing may not span the entirety of the distance between the bearing ends. As a consequence, a portion of the bearing near one or both ends is radially unsupported.
An unsupported portion is therefore exposed to shaft-imposed forces which may repeatedly deform and "fatigue" the end of the bearing. This can and does cause the bearing to eventually fracture around a portion or all of the bearing circumference. Machine downtime and a (usually) expensive repair follow.
Known journal bearings are made with a slight "corner break" or radius at the junction of an end face and the internal bore. Such a radius is provided to prevent fragmentation of tiny particles from what would otherwise be a rather sharp edge. As will become apparent, such a radius is unrelated to the invention.
An improved mechanical drive train having a journal bearing with a contoured surface to define a clearance zone between the shaft and the bearing would help prevent bearing fatigue breaking, excessive localized heating and wear and the formation of wear particles (all of which reduce bearing life), and, therefore, would be an important advance in the art.
This application refers to shafts which "deflect" or which are "deflected." As used herein, such terms refer to shafts which are bent, which are tipped or which, by a combination of bending and tipping forces, are made other than straight and/or other than axially aligned with a bearing.